Advances in semiconductor processing and logic design have permitted an increase in the amount of logic that may be present on integrated circuit devices. As a result, computer system configurations have evolved from a single or multiple integrated circuits in a system to multiple hardware threads, multiple cores, multiple devices, and/or complete systems on individual integrated circuits. Additionally, as the density of integrated circuits has grown, the power requirements for computing systems (from embedded systems to servers) have also escalated. Furthermore, software inefficiencies, and its requirements of hardware, have also caused an increase in computing device energy consumption. In fact, some studies indicate that computing devices consume a sizeable percentage of the entire electricity supply for a country, such as the United States of America. As a result, there is a vital need for energy efficiency and conservation associated with integrated circuits. These needs will increase as servers, desktop computers, notebooks, Ultrabooks™, tablets, mobile phones, processors, embedded systems, etc. become even more prevalent (from inclusion in the typical computer, automobiles, and televisions to biotechnology).
The power dissipation of a processor depends heavily on activity level, workload, temperature, operating frequency and other runtime variables. In addition to a single thermal design point (TDP) limit at which a processor can operate, a processor also provides a running average power limit (RAPL) feature. This feature can be used by customers to increase rack compute density (in the case of servers), battery life (in the case of client systems) or other power/performance/thermal constraints. However, available power saving techniques lose their efficiency as operating parameters are reduced.